1. Field of the Invention
The present invention relates to a motion sensing system and more particularly to a motion sensing system having short range capability for downward or outward looking, which system is simple, reliable and inexpensive.
2. Description of the Related Art
Motion sensing systems using passive infrared (PIR) sensors are well known. For example, such motion sensing systems are incorporated into light fixtures as a security feature and as an energy saving device. Examples of consumer type light fixtures having motion sensing systems may be found in U.S. Pat. Nos. 5,282,118; 5,434,764; 5,590,953; 5,598,966; 5,757,004; and 6,323,488.
Some of these patents concern movable motion sensing systems to compensate for uneven ground levels around an installed system or close placement of a sensing system to a heavily traveled street. These compensate when the system must be installed at higher than usual elevations or where ordinary street traffic interferes with the typical range of a system.
A common problem remains, however, in the region or space below an installed system. The typical forward looking motion sensing system, one having a line of sight outwardly away from a building, does not detect movement under the sensor. Often this non-monitored space is along the wall to which the system is attached. From a security standpoint, not being able to sense motion in the region along a wall is unacceptable.
The difficulties encountered in the past have been overcome by the present invention. What is described here is a motion sensing system placed so as to have a downward looking capability comprising a housing having an opening allowing a view in a downward direction when the housing is mounted for use, a sensor positioned in the housing, and a shield for mounting the sensor and for shielding the sensor from weather effects. In a simplified version the system includes a mounting, a PIR sensor having two side by side transducers and a blocking element to cover one of the two transducers from receiving infrared energy. Moreover, there is an absence of a Fresnel lens.
There are a number of advantages, features and objects achieved with the present invention which are believed not to be available in earlier related devices. For example, one advantage of the present invention is that the motion sensing system has a downward looking detection capability which is inexpensive, simple and reliable. Another object of the present invention is to provide a motion sensing system which uses a single mounting element for the look down feature. Yet another feature of the present invention is that the motion sensing system has a downward looking capability which uses a single mounting element that also provides a weather barrier around the sensor. A further advantage of the present invention is to provide the motion sensing system with a downward or outward looking capability which is structurally effective and cost efficient by using a readily available and relatively low cost two-transducer sensor where one of the sensor""s transducers is blocked. Still another feature of the present invention is to provide a motion sensing system for short range that requires no Fresnel lens.
A more complete understanding of the present invention and other objects, advantages and features thereof will be gained from a consideration of the following description of a preferred embodiment read in conjunction with the accompanying drawing provided herein. The preferred embodiment represents an example of the invention which is described here in compliance with Title 35 U.S.C. xc2xa7 112.